The number of opioid medications dispensed in the VA Healthcare System (VA) has more than doubled in the last decade. Almost 25% of VA patients receive an opioid medication from VA, and there is great concern about opioid overuse, overdose, and other adverse events. VA has adopted several strategies to mitigate the risks of opioid-related adverse events, but these efforts focus almost entirely on monitoring prescriptions dispensed within VA. More than 75% of Veterans have other forms of health insurance and can access healthcare and prescriptions in non-VA settings. Dual use of VA and non-VA health care and prescription benefits is likely to increase over time with the expansion of Medicaid and private insurance under the Affordable Care Act. The importance of dual use is magnified for opioid medications, which have unique risks that may be amplified when care is fragmented. In partnership with VA Pharmacy Benefits Management, the VA Center for Medication Safety, and the VA National Pain Program Office, this study will address this critical deficiency in the understanding of opioid use in Veterans. Ths mixed methods study consists of two quantitative aims (Aims 1-2) and one qualitative aim (Aim 3), that will be conducted in parallel. The aims are to: (1) describe the patterns of opioid use from VA and non-VA (i.e., Medicare, Medicaid) sources among Veterans receiving care in the VA and identify patient and facility characteristics associated with dual use of opioid medications; (2) evaluate the impact of dual use of VA and non-VA opioid medications on opioid safety and opioid-related serious adverse events; and (3) explore provider and other stakeholder perspectives on identifying and managing dual use of opioid medications among Veterans engaged in VA care. The quantitative phase will involve retrospective analyses of multiple linked datasets from VA, Medicare, and Medicaid for enrolled Veterans who filled an opioid medication from any of those sources. Analyses will examine the association between the source of opioids (i.e., VA only, non- VA only, both VA and non-VA) and patient and facility characteristics. Using propensity score and instrumental variable analyses and multiple mediation path analyses, we will examine the association between dual use of opioid medications and measures of opioid safety, including receipt of >100mg morphine equivalents daily, receipt of overlapping sedative/hypnotic medications, and opioid-related adverse events including overdose death and hospital or emergency room visits for overdose, drug delirium, and falls. The qualitative aim will complement these quantitative aims with two phases of semi-structured interviews of key stakeholders, exploring: (1) provider perceptions about identifying and managing dual use of opioid medications (Phase 1); and (2) the views of stakeholder leaders in VA, Medicare, Medicaid, and private insurance to interpret and synthesize the quantitative and qualitative results to maximize their relevance and impact on policy and future interventions (Phase 2). Together, these analyses will provide VA with timely and valuable information critical to understanding patterns, influences, and outcomes associated with dual use of opioid medications. The study will thus fill a crucial gap in evidence needed for development of optimal policy and clinical interventions to ensure the safe and appropriate use of opioids by Veterans.